Previously with ImageContainers, we would put the new preferred surface
into the ImageContainer. When we check if we should invalidate, it would
have a different image key, and hence invalidate the image frame and
schedule a paint.
With ImageProviders, it returns the same key in this case, because the
ImageProvider represents a particular surface. As such, we need to
actually track when we get a substituted ImageProvider, and invalidate
the image frame more aggressively to ensure we get the preferred size.
Differential Revision: https://phabricator.services.mozilla.com/D132583
